wicks



March 4, 1930. 1 WICKS 1,748,966

TELEPHONE TRUNKING SYSTEM Filed Sept. 23, 1925 4 5 Sheets-Sheet 1 22.7.27,"6 ,hC- -:/P-y/P/ /5 f M a 6) E y www SM@ 7 i 12M? w A /4 w @j F1 i l i 5 I IH Y -/a l:

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II/l' Jul-m Minka March 4, 1930. l J. wlcKs 1,748,966

TELEPHONE TRUNKING SYSTEM Filed Sept. 23. 1925 3 Sheets-Sheet 2 i i: iw@

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l--h-LLJ'EWIL D1"`- Jul-L11 Mwksv March 4*, 1930.

J. WICKS TELEPHONE TRUNKING SYSTEM VFiled sept. 23. 15125 3 Sheets-Sheet 5 I1-men :1P- Jul-m Musk 5 vPatented Mar; 4, 1930 y insiste A* i 'UNITED jfs-raras vimisNrf AOl'fFlaff n JOHN Wicks, or foAx PARK, ILLiNoIs, Assieivon, BY M'Esiviinss'ieniiinms 'ro 4vAUro- Y f Mario ELECTRIC.- INC., oF oHIoAeo,f1LLINoIs, Arconroaaiiioivos DELAWARE TELEPHoNErRUNKiNG sYs'rE-M i Application fudsepiemter 23.1825. serial No. 57,935.1

The present invention relates to telephone trunkingsystems in general, but is concerned more particularly -With trunkingsystems of y the type in which non-numerical trunk hunt- 5 ing switches are employed. Record ism'ade' of tlie Patent No. 1,528,751, issued March 10,

1925,'to Bellamy and Vicks.: y"llie 'broad general ,obj ect of the presentinve'iition is the production oinew and im-V v. `10 lproved circuit arrangements,iV rvwhereby vsec l ondary Atrunkingsystems of Ythe type described in the above patentare suitably rervised. to incorporate certain characteristics found to be useful in actual practice;

f Y Specilically, one object Cof the invention is concerned with the improvement of the operation fof the?v secondary switches sol that .29 primary sub-group, the likelihood of .a falseV Wh'en'an idle one is taken for use,` at a time when others vare hunting Within the same operation ofthe rotary magnet of the seized switch is eliminated. f A further-object of the 2 5 rangements whereby the'f-relays. ofthe secondaryswitcliesimay be removed from the switches themselves and placed on the prif,

mary side vofthe intermediate.distributing frame in order thatv all the relays of'c'ach 30 primary sub-groupy may be mountedr as a unit. yThis makes the running of the chain circuit for controlling the starting of the secondary switches a much simpler operation.

Y `rrnotlier object of the invention-'is to adapt the circuits so that the vso-called individual and common truuking arrangement maybe applied to the primary subgroups. To thisV end, a double V'chain-circuit arrangementhas secondary lswitches in the vsame sub-group to hunty successively'y until( the'congested condition has been relieved.

UA' A,feature lofv the invention-` relates to'y the provisional? aplastar associatedfwththe 'Chain invention 'is the production of new Aand improved circuit ar-V relay equipment-or indicating when all the Y trunks in a given primary sub-groupk become busy. v Y

1 Referring now to thedrawings comprising Figs. 1 3, inclusive, these drawings show, by means of the usual circuit diagrams, a certain amount of Yappi'iratus ina telephone sysj tem embodying"thejpri-nciples of themven-j tion.. 'Iii order for the .drawings to be' un* derstoodbest, Fig. 2 should be placed below 1, and Figl should be placed tothe right of Fig. 1. When the drawings arejthus laid. out, Figs. land 2 showtvvo primary'su'bgrou-ps of .trunks Withtheir vcommon equip'- vment,`and F ig.k 3 shows a portion of a single Asecondary sub-group,v together With certain equipment common to the sub-group.v Y The terms primary sub`-grou1: .and Seoondary sub-group7 'Will beundersto-odupon reference to the above mentioned patent.

ARel-f erringnovv particularly to'Figs. 1 and 2,

Athe vertical row of terminals at the left'ofthe tivo sheets and'labeledT. A. at the-top of Fig.' 1 represents terminals at` the so-called terminal assembly which is the name comvin'onlyused to designate the Vramefat Which the multiply connected'bank terminals of v a 'number o groups'of selectors terminate.l It is `at thisgirameA that the 'connections determining the number o'f'selectorsto feed traI-lc 'int-o' a given'primary sub-group aremade.

The relays and'ot-her equipment, together with the associated vertical rows ofterminals occupying the centralpportion extending verl.

tically through thetvvo sheets, are' labeled f Relay rack in Fig. 1 Trunk cableszaref run from the terminal Vassembly T. A. to .the left-` hand sideof the relay rack, and other trunk cables are runfrom the right-hand side vot tlierelay rack to the left-hand side of the intermediate'distributing'frame I. D.; F. 'itis atjthe I. D.. F. that lthe jumpers are run to cross-'connectthe various trunks inthe respective primary sub-groups With switches in 'the desired 'secondary sub-groups.

From the right hand side of the I. D; F., the cables' extend to the secondary svvitches,"one of which (the secondary switch SS.) isshown nated T-l and T-1(). From this, it will be understood that these two trunks are the iirst and tenth trunks, respectively, ci a group of ten trunks accessible to a group of selector switches. It will be noted that the usual chain ci 1cuit is provided, extending through contacts on the chain relays of all the trunks in the primary sub-groups, whereby the chain relay 19 is operated to control the start relay 20 in the usual manner. The chain relay 19 is marginal, and is so adjusted that it does not operate with two of the resistances, such as 10,

connected in series in it. vWhen all the resistanc-es, such as 10, except 1, are shunted, relay 19 (which is also a two-step relay) energizes throughits first step and operates the start relay 20. `When all resistances are shortcircuited, relay 19 operates through its second step also, thereby 'operating the meter M so as to register the condition of all trunks busy within the subgroup. It will be noted that the start relay 20, upon operating, closes a point in the circuit of the stepping magnet ot each of the associated trunks, so that such secondary switches as are idle and are standing on busy outgoing trunks'operate to select idle trunks.

It willV be noted that F ig. 2 shows two trunks T-l and T-10, respectively. These latter trunks vare the irst and tenth trunks, respectively, of a separate primary sub-group. It will be noted that the trunk T-10 is not provided with a line relay and that the line conductors are not closed through at the terminal assembly T. A. instead, the trailic intended for trunk T 10 is diverted through the conductors 31--33 to the trunk rI`-1O, Fig. 1. That is, the trunk TNlG, Fig. 1, is common to two groups of selectors. This is the well known scheme employed for obtaining aV greater trunking efficiency by making certain trunks individual to each ot two groups of switches and makingcertain other trunks common to the two groups, the individual trunks being first choice to the switches concerned and the common trunks being chosen by a given group of switches only after all the trunks individual to that group are busy.

Referring now particularly to Fig. 3, the secondary switch SS shown therein is mechanically of the well known type of switch in which the wipers have no normal position and in which the wipers are advanced upon the back stroke of the associated stepping magnet instead of upon the front stroke. `Although the switch SS is shown diagrammatcally as having only a few contacts, this switch is assumed to have (and in the layout herein disclosed does have) twenty-live sets ot bank contacts. rlhe control switch GS, from a mechanical standpoint, is similar to the secondary switch SS It is assumed, in the present case, that the tratlic 'imposed lon Vthe 'group of ,outgoing trunks is such that eighty secondary switches, such as SS, are required to suply traffic to twenty-tive outgoing trunks', it being assumed that the secondary switches, such as SS, have access to twentyiive trunks cach, although only a iew oil the bank contacts of this switch are shown. It is assumed further that the secondary switches are mounted in rows oi' twenty switches each, each row being termed a sheli. There is provided one battery-feed relay, such as 211, for each of the four shelves of switches, makin o' 'our battery feed relays per sub-group. lso, there is provided, Vfor each shelrn of switches, two cutofi relays, such as 215 and 216, the relays 211, 215, and 216 being assigned to the shelt' in which the secondary switch SS is located. The func-tion ot the battery "feed relays, such as 211, is to start the common control switch CS, which controls the hunting operation in the diii'erentshelves when more than a predetermined number ot switches start hunting.

In the patent hereinbefore referred to, `an arrangement isdescribed, whereby, when all thetrunks outgoing from a particular sub group are busy, a cut-olil relayis operated to disconnect batteryfrom the operating magnets of all the switches having access to the busy sub-group. The cut-oif relays, such as 215 `and 216, and the' cut-off relays (not shown) for the other shelves Correspond to Y The same cut-olf relays are employed in re-V stricting the hunting movement under the control or the switch CS which operates to permit hunting by a small number of secondary switches at a time in a manner to be pointed out hereinafter. A

The invention; having been described generaly, a detailed description of the operation of the apparatus disclosed will now be given. VFor this purpose, it will be assumed that the trunk T-1, Fig. 1, is seizedby one ot` the selectors having access to it.

lhen the trunk T-l is seized, a ground potential is extended over the release trunk conductor 3. through the terminal assembly T. A., the relayv rack, and the I. D. F. tothe release trunk conductor 16 of the secondary switch SS'. Since the test wiper 20a ot the switch S'S is standing on the test contact'of the repeater R, the ground potential is eX'- tended to the release trunk conducto-r 2520i the outgoing trunk, thereby making the trunk comprising conductors 2514-253 busy in the extendingvto the distant oli'ice, with the result "f'usual manner. As a' further result'of fthe i 'loclr-l-ng-circuit'tor its lower winding at armabefore the operation ofarm'ature 13 otrelay l 9; "As afurther result oih the'energization of seizure of the trunk T-''1, a circuit'is closed oV'e-rconductors 2 and 41 through the termi-U nal asseinblygT. A., the relay'rack, the l.l D. F., conductors 15 'and 18, .wipers 203 and 205, and

conductorsV 251V and 253 rfor the line relay 206V oi' the repeater R. rllhe upper'winding ofthe line relay S" at the relaylrack is included in the circuit 'ofr the line relay 206,' with `theresult thatv relay 8lenergizes"and.. at armaturev 12, opens a vpoint inl thecircuit of they stepping magnet 201 of the secondary switch SS, and

closes a locking circuit for itslower winding. :At armature11,.relay 8 vshort circuits its up lper' winding subsequent to theclosure of the ture12. I,The chainfrelay-=9 is energized-re- 'sponsiveto the placing ofV the ground potential on the release trunk conductor of the trunk-T-1' and-,closes at armature 13 apoint inthe circuitof.the'steppingmagnet 201 oic :the secondary switch SS, 'Thisdoes not result in the closure of the' circuit ofthe stepping magnet of the secondary'switch SS ow-r ing tothe fact that the adjustment of therelays 8 and 9 isl such that relay 8 opens a point in the steppingmagnetcircuit at armature 12 relay the resistance 10 `is short circuited Aat armaturelltso asto bring about theopcrationo relay 19 in a manner to Abe pointed out hereinafter.'

In the'repeater R, Fig. 3, line relay20 energizes when'its circuit'iisfclose'd' andfit closes at armature 208 the usual control circuit for the switch to which the outgoingV trunk extends, at the .Sametime `closing` at yarmature 254 a circuit for yrelease relay 207. yRelease relay 207 energizes Vand places ground on release trunk conductor 252 at armature chain circuit, which operation ,does not proare other trunksxin thesainelsub-group that are not in use.' n, y

, ln response to Vthedialling of ytheremain- 'ing digits in the desired number, the inter-y t. rnptions thereby producedin the circuit of ,Y line relay206 of the repeaterR are relayed i to the associated,.inter-oflicetrunk'at armafture 2.08, whereupon the connection isA exr `55 tended tothedesired line vin the usual man'- 11611 Upon the termination lofthe ensuing con- "rersati'on, the call-ing subscriber replaces his receiver', whereupon vline relay 2,06- alls'bacli and opens at armature 208l the control circuit that'the switches inthe ldistant oilice are released in thel usual manner.' The circuit kvot release' relay207 is opened at armature 254C 'andelay .207'v -falls rhaeltafter an Y' interval standing' on abusy trunk.-

9, outer contacts of relay 20, connections at release trunkconductor252- When this oefV curs, the relays E5y and 9, Fig. 1, a'll back, reistoringnthe associated circuits to the position `shown in the drawings. Also, the precedingff* switches 'are 1 released inl the usual manner.' lit willy be -understood that the chainfrelay 9operates1whenever the Vassociated release trunk conductor is grounded whether this is due to the trunk T-1 being. taken vfor use or to the fact that the secondary switch SSi's and. removes groun'df at armature 209 fromk l Assuming now Vth t nineof the` ten' trunks'.

of thepriinarysub-group shown infFigl are busy to the selectors having accessfto them, lwhich conditioncoines about' 1n the` `case of anyone trunk if that'trunkis' actually in use or i'f'the associated secondary switch is standing on a busy trunk, the marginaltwo- Vstep relay 19 operates through its first step,l

operating the armature 2l to close a circuit for relay 20. l The' .second step "armature 22 yis not operatedatthis time.v Relay 20,'upon il energizing, closes points vin the circuits of the vten associated stepping magnets, such asftheiV stepping magnet 201,.Fig. 3f,`of thesecondary switch SS.y Accordingly, such switchesof this primary sub-group as are'standing ,on`

kbusy trunks `Vand are notv themselves Vbusy Y, start searching for vidle trunks. The stepping A' circuit for the'secondary switch SS, for. eX-

ample', in case that switch is idleand is vstandr vingonabus'y trunk is as follows: from ground by way of the busy test contact encountered .v

'icoA by testwiper204 otl the secondary switch SS, i release trunkcondu'ctor 16,'con'nections at the I. VVD. F. and at the relay rack, armature 12 vand'its resting Contact otrelay .8,workin`g.

contact and armature' 13 o1' the cha-in `relay' the l. D. F., yconductor 17,v resting'contact and armature217 of the cut-oli` ,relay 215, f Fig. 3, interruptor contacts 202', lstepping `ii'iagnet 201 of the 'secondary' switch SS, relay Y 211,.and the associated fuse to battery.l Stepping magnet 201, under' the control of its, self-interrupting contacts 202, [advances the v`wipers-203--205 step byy step in 4Search of an idle trunk. This operation c'ontinuesuntil an .l-dle'trunk is found, or untilvrelay 20, Fig.

1, falls back, which it may do prior tothe completion or"Y the operation of the secondary y cessful prior to-thelarrival of thewipers 203-205 on trunk. ff, When van. idle trunk is vfound by one of the searching secondary switches', the chain: relay l .Toif'vthetrunlr` associated with the successful switchfallsbacl and introduces a sec'on'dreg sistancein the circuit of relay 19, whereupon Y the bank contactsof an 'idle 4switch SS in c'ase some other switch issuc- Y,

relay 19 is restored to the psitionshownin )Y the l drawings, openingv the circuit of relay 20. Relay V20 thereupon jr'ialls back and-o'pens all; thel associated stepping magnet circuits.

-It will be noted that for the purpose of keeping two idle trunks pre-selected in each primary sub-group, the trunk '1?"10, Fig. 1, belongs to the primary sub-group illustrated iiiFig. 2 as much as it does to that shown in F ig. 1, being commonv to the two sub-groups. Accordingly, when ground is placed on the release trunk conductor of the trunk T-10,

.Fig.`1, a ground potential is extended over conductor 32 to the release trunk conductor of the trunk T-*10, Fig. 2. The result is that the chain relay on the trunk T-lO operates simultaneously with the operation of the chain relay on the trunk T-lO, Fig. 1, so that the chain relay contacts in both subgroups are closed when the trunk is in use from either of the two sub-groups.

`pull up the start relay 2O and the last remaining trunk is taken for use before a new one can be preselected, the last reniainiirgresistance in the circuit of relay 19 is short circuited, whereupon relay 19 operates through its second step and closes a circuit for the meter M to register the momentary condition when all the trunks in the sub-group are busy tothe associated selectors. An occasional operation of the meter M, therefore, will not indicate an abnormal state of affairs, but, in case the subgroup is consistently overloaded, the frequent operation of the meter M should indicate the fact. Referring now to the operation ofthe control equipment shown in Fig. 3, it has been found in practice that, when there are only two or three trunks idle in a given secondary sub-group, there is a tendency fora great number of idle secondary switches to pre- 'select the same idle trunk. Now in case the conditions are somewhat congested at the corresponding primary sub-groups, most of the idle secondary switches ofthe large group collected on the same trunk start hunting siniultaneously when the idle trunk is taken for use by one of these switches. T his leads to two diliiculties. In the first place, the ground potential is supplied to the release trunk conductors of busy trunks through relatively-light relay contacts, with the result that these contacts are often unable to carry safely the comparatively large amount of currentnecessarytoenergizethesteppingniagnets of a large number of secondary switches. Furthermore, the test wipers of the secondary switches are ofthe bridging type, i. e., a test wiper encounters the next Contact before it breaks contact with the one which it is leaving. Accordingly, when the large number of switches are rotating synchronously, `with one switchlagging slightly behind, the test wiper of this one switch suppliesground to energize the stepping magnets of all the other switches in case the group of simultaneously operating switches is just passing from a busy trunk to an idle one. r1`his sometimes results in the test wiper of the lagging switch becoming damaged due to the excessive current carried by it. Y

This condition is remedied in the present case by restricting the limiting action when it becomes too congested within a given secondary subgroup, as will nowV be explained. lt may be pointed out that the battery feed relay 211, which supplies battery to the inotor magnets of a shelf of twentysecondary switches, is adjusted so that it does not operate until a pre-determined number of'secoiidary switches in the associated shelf are Y operating simultaneously. It has been found in practice that in iiiost cases, the best control of the limiting operation of the switches is secured with the relay 211 adjusted so that it will not operate with three switches rotatingV butwill operate in case four switches are rotating in the associated shelf; When this condition arises in the shelf associated with relay 211, the said relay operates and at armature 212 places battery uponl the conductor '213 common to the battery-feed relaysV of the four shelves of the secondary sub-group., Relays 231 and 232 both operateover conductor 21,3 and over their lower and upper windings, respectively. At armatures 263 and 264, relays 231 and 232 close locking circuits for their upper andlower windings, respectively7 through the resistances 267` and 268. At the two upper armatures of relay 231, relays 215 and 216 are disconnected from the common conductor 214 and are connected to ground through the resistances 265l and 266, respectively.'V Relays 215 and 216 energize and open the associated stepping magnet circuits. rlhe cutoff relays of the second, third, and fourth shelves of this sub-group are energized siniiliarly. y p

At armatures 261 and 262, acircuit is closed .for the upper winding of relay 220. Relay 220 energizes and closes at armature 224; a

circuit through the resting contact and armature 222 for the slow-to-pull-up relay 218. A circuit is closed through. Contact 234 of stepping magnet 233for relay 219 with the result that relay 219 operates and opens at armature 222 the circuit of relay 218 before relay 218 has had' time to operate. A further` circuit is closed through the resting contact and armature 221' for steppingmagnet 233 of the control switch CS. Stepping magnet 2.33l energizes preparatory to advanciso 1 .ingthe wipergees andere mid at @mais 234; opens the circuit of relay 219; Relay 219 now rfalls back andv atarinature 222y again.

'closes the circuit yof the slow-to-pull-up relay;- 218, with the result that relay218 energizes after a Aslightinterval Yand'opens at armature Y 221 the circuit-of niagnet233. Magnet 2.33

` falls back and closes'at contacts 234ithe circuit of .relay 219 at the same time advanc-v ing the `wipers 263and269 one step'in a counter-clockwise direction.l kV-ipefr 269 `closes a .circuit through 'the first associated bankfc'ontact for the lower winding ofgrelay 220 so as to maintain-.this v.relay energized until; the controlswitch CS .has completed its cycle otoperation. Wiper 268, however,

lencountersga dead -'contact' and does? not, therefore, produce .any result lat this time.

' This dead contact is placed ingthebank of 'the wiper 268 sov as to delay the control ofthe hunting oper-ations vuntil theoperationpf the interrupting relays218rand 219l has become steady, aslthis operationfinay be` somewhat irregular' untilltheirst two'steps have been taken. I y fr, Y i .i .e

4Responsive to the closureo the Acircuit of net 233 again: flfThe' resultisthat magnet pullsup preparatory to a. further advance of thefassociated wipers, andga't armature 2311 I opens the circuit "ofyrelay', 219.1V AR 3layj-219 again falls back'jwith"the result that relay Y 218 pullsrupYa-nd opensat armature 221 the' circuit of steppinggmagnetj233, whereuponl Vsecondary trunks andfin which aninterme'di.-l v

' .stepping .ma'gnet'2331 fallsiback and advances' n,the-wipers263)an'di269, one step. Viper 268,

at lthis time,v placesbattery on the junction of cut-ofrelay Y215 andy the,l resistance'265,.A The result is that cut-'0Hl rela-37,2145 falls back and closes points linthe circuitsof the ten associated secondary switchessoy that the ones that 'are attempting to hunt may nowy doso;

i TheoperationoftheswitchgCS underithe l L switch, a trunk line terminatingv in .said i switchand including.atestconductona stepi control of vrelays 218 and 219 continues in the lmanner described,with the result that upon the next step vof-wiper268, relay 21.5vv is again I energized and relay r 21d-is deenergized .in .itsV stead.v `Upon the next-,two v succeeding'steps, .thecuteoff relaysiofthe'second shelfA are deenergize-d, momentarilyL i and, uponthe fifth vrefective1st-ep ofwiper 268, thelocking winding of relay 231 is short circuited,"whereupon relay V @Upon the` 'succeeding stepsot the control 'switch ,CS,the1our cut-OE .relays of .the third and. fourth shelves are successively deener- `gized, after* which theA locking. winding of relay 232 is; shorticircuited.` f 232 now f rWhat isy claimed is: y. l 1. n-a telephone system, a group of primary trunks divided into sub-groups, a group' I voi: secondary trunks ydivided into sub-groups, 7

"said secondary switches. f

.231.falls-back. and permits the cull-Uff' relays of `the tirsttwo shelvesy to fall back in I se batterV has been removed. irom conduc-. .i Ca' y 1 f i- 'l aniotormagnetfor said switch, a circuitfor Y saidinagnet, means controlled voye'r said talkving conductor responsive to a vseizure of said trunk line for opening one point in said ci`rductor for closing another point in said cirfof course,l thaty in' case the* congested condi- 1,76

tion remains at'one of the shelves,.relays 231 and 232 remain energized andthe V,above yoperation is repeated.

Assuming, however, 4 pearsjfrom thecommon conductor 213 prior to the'short circuiting of thelocking Ywinding*` .of-lfreiayZBlfand-,that lrelays 231 and-232are now -both deenergized, the initial energizing .circuit of relay 220 lis now open at armatures. 26.1 and 262. Relay 220 remains energized lthrough itslocking circuit, however, untilv wiper-269 takes another step and lands on'the the wipersin this position.' l

separate,y subfgroups l.of Vsecondary `switches dead contact shown.` 'The nextcycle'y of oper-l` `ations of the control switch CS begins with f., Y,

having access to saidsecondary-trunk sube' 1 groups,respectively, a distributing framelat i.

,which said primary trunks terminate and,V

from whichconnections are made. to said sec- `Orlrdzrry 4switches,1said frame.includingjump#V 'i ers forconnecting any desired primary trunk f with any desired secondary switch, and re-v lays, connectedfwithV said .primary. trunks.v

ywhereby,saidsecondary switches are'. con-,fv

trolled saidrelaysthroughsaid jumpers.. 5100 Y 2. yIn a non-numerical trunking systeniin which the primary ytrunks t'erminateinnon-`v numerical secondary switches having access to i atedistributing frame is provided vthrough 'which' the.Y primary trunksare connected by c lmeans of ).umpersfto the secondary switches,

two relays connected in each of'said primary trunks on the primary trunk .side ofthe int'erinediate distributing frame vfor controlling ping magnet for said switchhavingacircuit rconductor to closela pointk in time thevrelay is operated. 4.'.111 atelephone system, 'a

trunk line inincluding saidtestconductor, a relay perma-4 'nentlyconnected to said testconductonjand i. .means for operatingsaid relay over said test, y

said .circuit each` -1` cludinga tall'ring conductor and aftest conductor terminating in an automaticy switch,

cuit, and v*means controlled over said testc'onswitches,

'cuit whenever a busy potential is present on 'the test conductor. Y Y

5. In a telephone system, atrunk line terminating inan automatic switch and coinprising two talkingrconductors and a test conductor, a relay connected tol one ot said talking conductors, a relay connected to said testconductor, a motor magnet for said switch,'acircuit tor said magnet, said cir cuit including normally closed contacts on the lirst named relay and normally open contacts on the second rela-y, and means responsive to seizure of said trunk line for energizing both o1"- said relays.

VG. In a telephone system, two groups ot trunk lines accessible tov two groups of aectively, another vtrunk line accessible in common to both grou )s of switches,

PGS

chain relay 'for the iirstV group'ot switches, a chain relay for the sec-ond group ot switches,

circuits tor said chain relays, a relay indi- Widual to each ot the trunk lines accessible ondary switch accessible in commento bothA groups ot primary switches, means associated with the first group of primary switches for controlling Vthe hunting action ot the associated secondary switches, and similar means associated with the second group ot' primary switches, lboth ot the last named means including means if'or controlling the limiting operation ot the secondary switch comnion to both primary groups.

8. In atelephone system, a group off scc ondary switches accessible to a group of primary switches, a two-step relay common .to the secondary switches operable through its r'irst step to control the hunting action of the secondary switches when'only one secondary switch is idle to the primary switches and operable through its second step when all ot said secondary switches are busy to said primary switches, and an indicating device operated each time said relay operates, through its second step. Y

9, In a telephone system, a group o' automatic hunting switches, said group of switches being divided into sub-groups, counting control apparatus common t-o the group, means responsive to an abnormally congested hunting condition within the group tor starting said control apparatus, and means controlled by said control apparatus tor stopping the hunting operation in all said Vrsub-groups and for permitting the hunting numerical switches having stepping magnets and` having access to secondary trunks and in which an intermediate distributing trame isY `provided through which the vprimary trunks are connected byA means of jumpers to the secondary switchescircuits for the stepping vmagnets of the` secondary switchesfincluding said jumpers,l and relays connected in said primary trunks on the primary trunk side of the intermediate distributing Atrame tor controlling said stepping magnet circuits. V l2. In a telephone system, a group offsecondary switches accessible to a group` of primary switches, a control circuit common to the secondary switches, means controlled over said lcontrol circuit when only one secondary switch is idle for starting afhuntinfrfaction Within thesccondary "group, an indicating device, andmeans controlled over said Vcontrol circuit responsive to all secondary switches being busy tor-operating said device. 13. In a telephone system, av pluralityof groups' ot trunks, a'pluralityv of automatic hunting switches, one for each trunk, each trunk including a test conductor, means for placing a busy potential on anytest conductor under Ypredet'ermine'd idlevconditionszot the associated trunk for rendering the trunk non-available, means eiective responsive to the existence of alpredetermined minimum number of available trunks in any group 'for f causing the-operation of the hunting switches of the idle trunks of the particular group, and limitingmea'ns forjlimiting thesimultaneous hunting action to apredeterrnined maximum number or1 groups. Y

14W. In a.V telephoneV system, a plurality of groups or trunks, a'plurality of automatic hunting-swit`ches, one for eachtrunk, each trunk including a test conductor, means for placing a busy potential on any test conductor vunder predeterminedidle conditions of the associated trunk for rendering the trunk non-available, means effective responsive to the existence of a` predetermined minimum number oit available trunks inV any group Yfor causing the operation or" the hunting switches ofthe idle trunks of the particular group, and limiting mea-nsfor limiting the simultaneous hunting action to a predetermined which the primary trunks terminate in -non,

maximumV number of groups, said last means including means responsive to the tendency I' hunting operation to proceed thereafterin- `said groups one at a time.

to exceed said predetermined maximum number for stopping the hunting operation in all fof fs'aid groups and vitor permitting the '15. VInV a: telephone system, a plurality of trunk lines, each including'at least vone talk- -ing conductor and a test conductor, a plurality of automaticswitches, each terminating one of said trunk lines, each 'switchincluding a motor magnet, means in each trunk line controlled over the talking conductor ofthe @trunk responsive to the seizure of the trunk for lopening a point in the circuit of the motor magnet of the associated switch, and

Y means in each trunk controlled over the test u conductor of the trunk Vindependent of the .other trunks for closing anotherpoint in the same circuit.

16.V In a telephone'sy'stem, plurality of 'I trunk lines each including atest conductor, a

n, plurality of secondary line' switches each terr minatingone of said trunk lines, eachswitch including a motor magnet controlled over a vcircuit including the test conductor of the associated trunkline, `a-relay in each trunk line, and means in each trunk line controlled "by the associated` relay independent of the corresponding relays of the other trunk lines v to close a point in said circuit of its associated Y motor magnet.

177.v In a telephone system "a group of pri- Vmary trunks yeach. terminating in an automatic switch, a plurality of,y secondary trunks .accessible to each switch said lswitches being v of the type that arenormally in selective po- I sition with respect tosome secondary trunk,

a circuit for controlling each ofsa'id switches,

means in each trunk eifective responsive tok the seizure'of the particular trunk with which `the'associated switchis in selective'position for closing apoint in the circuit of its` associatedv switch, means responsive to the exist-f.

ence of predetermined conditions in the group of'primary trunks for lclosing another point Y inthe circuit of eachofthe' switches, and meansl vresponsive-tothe seizure of any primary t-runk for opening a point in the circuit; of itsassociated switch, said threeppoints inY eachcircuit being lconnected in series.

'178. In a telephone system, a plurality. of

primary trunklines each terminating in an automatic switch, ya plurality ofrsecondary trunks accessible to each switch, the switches being of the typethat are normally 'iii` selective position with respect to some secondary its associated switch responsive to the seizure' of the particular'trunk with which fthe associated switch is in'selective position.

yside of the frame.

19. In a'jtelephone system, a group orprimary trunk lines each terminating in an. auto-v .matic switch,A a group of secondary trunk lines accessible to each` switch, a magnet for each switch,means responsive to the exist-fl ence of predetermined,conditionsin the group n V of primary trunks for closing one point in 1 the circuit of each magnet, means responsive tothe existence of predeterminedk conditions in any groupjof secondary trunks for open-' ingV one pointinfthe magnet circuits Vof all the switches having access to that group of secondary trunks, and means responsive to the seizure of a secondarv trunk Vior closing i 80 one point the circuit ofthe magnets of the.`

{switches that are in selective 'relationship with that particiilar secondary trunk,-said three points being series. K

20. In a telephone system, a pluralityzof primary trunk lineseach'ter'minating in an automatic switch, a motor magnet for. each switch,a plurality of secondary trunks ac- ,A cessible to each of said switches, said switches Vbeing normally in selective relationship with f some trunk,jmeans responsive to the existencey of predetermined conditions. in 'theVV group of primary trunks for closing one point in the circuit of each ofjsaid magnets, means responsive to theV seizure of a secondary trunk for closing another'point in the cir-V..

are in selective relationship with that secc5, f cuit ofthe magnet of only those switches that 'i ondary trunk, 'and means responsive to the c seizure of any primary trunk for openingv a third point in the circuitof its magnet,y vsaid s three points vhein'g connected in series.

.21. c In a telephone system, an intermediate distributing frame, an automatic trunk hunting switch, a' trunk connected to said switch through the lintermediate distributing rframe i so as to make the switch individual to the trunk, and a magnet controlled by a plurality of relays individual to the trunk for operating said switch iii its huntingmove ment, all of thel relays that control the mag-Y net andare individual to the trunk being on one side of the intermediatedistributing frame and the magnet being on the other 22. In a telephonesystem, twolserially re-k lated trunk line's,a switchv individual to the irst `trunk line,'bank contacts individual toV j thesecond trunk line engagedby the wipers of said switch, a-circuit establishedresponsive to the seizure of said irsttrunk line, i1-

said circuit including the two talking ycon-V yductors of both trunk lines in series, a conv trollingrelay for said switchzincludedin saidcircuit, and a distributing frame carrying jumpers which are included in said lirstV triinkline between the saidcontrolling relayj y and `said switch.

2 3; In a telephone system, va trunk line teri minating vin an automatic switch, a second `trunk line terminatingin `a repeater, 'a line iso a' ico,

'elay for Controlling said switch, a distribut- 'ng frame, a Circuit including a j urnper on aid frame over which Said Control is exercisedVa line relay in seid repeater, and a circuit including a talking conductorof each trunk line for energizing both line relays in series.

n Witness whereof, I hereunto subscribe my name this 21st day of September, A. ll,

JOHN VVICKS. 

